Lubrication Prepared By Dr. Biswajit Saha

Emulsion lubricants The lubricants used in the form of emulsions are termed as emulsion lubricants. An emulsion is a colloidal dispersion of two immiscible liquids in which one liquid acts as the dispersion medium and the other as dispersed phase. The Emulsion are two types Oil in water (O/W) type (oil acts as dispersed, water act as dispersion ) Water in oil (W/O) type. (water act as dispersed, oil acts as dispersion )

Oil in water (O/W) type: (Cutting emulsion or cutting oils): they are prepared by mixing an oil with suitable quantity in the presence of 3-20% of water–soluble emulsifing agent such as a water soluble soap, alkyl sulphate, alkyl or aryl sulphonate. Use coolant cum lubricant for cutting tools Water in oil type emulsion (Cooling liquids): This types of emulsions are prepared by mixing water and oil in the presence of 1 to 10 % of water–insoluble emulsifying agents such as calcium metal soaps. Used for steam cylinders to keep the wall cool with less oil consumption.

Viscosity: Viscosity is a quantitative measure of a fluid’s resistance to flow SI unit of viscosity is the pascal-second (Pa·s), (equivalent to (N·s)/m2, or kg/(m·s)). Factor effecting on viscosity Temperature: Viscosity of liquid decreases with increasing the temp. Because increases the K.E of the liquid hence the intermolecular attraction decrease. Pressure : viscosity increases with pressure. Because volume decrease with increase the pressure hence molecules come close each other iii. Nature of liquid: The liquid having stronger intermolecular forces of attraction are expected to have more viscosity. Alcohol have higher viscosity than Benzene

The coefficient of viscosity (η): Defined as the tangential force Required per unit area to maintain unit velocity gradient. Unit is Nm-2 Viscosity index The rate at which the viscosity of an oil changes with temperature is measured by an empirical number, known as the Viscosity index (V.I.) The viscosity index is calculated by the following formula: V.I. = (L - U)/ (L - H) x 10 where , VI is viscosity index U is the viscosity of the oil under test at 100 °F L & H are various values based on the viscosity at 100 °F of low and high viscosity standard oil.  

Determination of viscosity by 'Redwood Viscometer' Redwood Viscometer' are of two types: 1. Redwood Viscometer No.1 (For fluid having viscosity corresponds to Redwood seconds less than 2000) 2. Redwood Viscometer No. 2  ( For fluid having viscosity corresponds to Redwood seconds greater than 2000) The difference between Redwood Viscometer 1 & 2 are the difference of orifice diameter.

Fill the oil cup with oil to the required oil level indicated by marker point Heat the water at uniform temperature. When required temperature of oil is attained, lift the ball above the orifice hole. Allow the oil to pass through it (start the stop watch) and collect 50 CC of oil in the volumetric flask. The measured seconds is in terms of viscosity of oil measured.

Flash and fire-points: Flash point is defined as the lowest temperature at which the lubricant oil gives off enough vapour to give a flash when the vapour come into contact with a test flame. Fire point is defined as the lowest temperature at which the vapour of the oil burn continuously, at least for five seconds when the vapour come into contact with a test flame. A lubricant should have flash point above its service temperature to safeguard against risk of life. Determination of flash and fire point of a lubricating oil are usually Determined by using Pensky-Marten’ apparatus.

Pensky Martens Flash Point Apparatus: Use for determination of flash & the fire point of fuel

Fill the cup with the material to be tested up to the filling mark Fill the cup with the material to be tested up to the filling mark. Place it on the bath. Fix the open clip. Insert the thermometer of high or low range as per requirement and also the stirrer, to stir it. Light the test flame, adjust it. Supply heat at such a rate that the temperature increase (5oC per minute). Open flash point is taken as that temperature when a flash first appears at any point on the surface of the material in the cup. After flash point, heating should be continued at such a rate that the test flame causes the material to ignite and burn for at least 5 seconds. This is the fire point.

Cloud points: When oil is cooled slowly, the temperature at which it becomes cloudy or hazy in appearance, is called its cloud-point. Pour point is the lowest temperature at which the oil just ceases to flow It is important because the suitability of lubricants in the machine working at low temperature. It indicates the lowest servicing temperature below which the circulation of the oil is unreliable and inefficient, causing wear of machinery. Oiliness: Oiliness is the ability of lubricating oil to stick on to the surfaces to be lubricated under conditions of high pressure or load. Lubricants with good oiliness stick on and remain between the surfaces even under higher operating pressures.

Aniline point: Aniline point of an oil is defined as defined as the minimum equilibrium solution temperature for equal volume of aniline and the oil. Thus aniline point refers to the temperature at which equal volumes of aniline and the oil to be miscible. A high value of aniline point indicate the presence of a lower percentage of aromatic hydrocarbons in the oil

Saponification What is saponification??? On refluxing with alkali, triacylglycerols (fatty acid esters) are hydrolyzed to give glycerol and sodium/potassium salts of fatty acids (soap). Such process is known as, Saponification.

O Break the ester linkages C – O- by hydrolyzing the bonds between the carbon backbone and the fatty acid chains. (Reversal of esterification reaction) Form the sodium salt of a fatty acid (soap) and a trihydroxy alcohol (glycerol). The saponification value is the number of milligrams of KOH required to neutralize the fatty acids resulting from the complete hydrolysis of 1g of fat.